Homeostasis and Response

• Homeostasis


  Maintaining a Stable Internal Environment
• Homeostasis


  • It is normally important because your cells need the right conditions in order to function properly
  • The conditions inside your body need to be kept steady, even when the external environment doesn’t
  • including the right conditions for enzyme action
• Homeostasis


  1. Regulation of the conditions inside your body land cells to main

  2. asb.internal.onisnment in response to changes in both internal and external conditions
• Automatic control systems in your body


  • They include both nenous and hormonal communication systems
  • They maintain your body temperature
  • They maintain your blood glucose level
  • They maintain your water content
• Automatic control systems


  Made up of three main components: cells called receptors, coordination centres including the brain, spinal cord and pancreas, and effectors
• Negative Feedback


  1. Receptor detects a stimulus

  2. The coordination centre receives and processes the information, then organises Asponse

  3. Lecker produces a response which counteracts the change and restores the optimum level
• The effectors will just carry on producing the responses for as long as they're simulated by the coordination centre. This might cause the opposite problem- making the level change too much away from the ideal. Luckily the receptor detects if the level becomes too different and negative feedback starts again
• The Nervous System


  It means that humans can act to their surroundings and coordinate their behaviour
• The Nervous System


  • It Detects and Reacts to Stimuli
  • Organs need to respond to stimuli ichanges in the environment in order to sa
  • Single-celled organism can just respond to its environment, but the cells of lar organisms need to communicate with each other int
  • As multicellular organisms evolved, they developed ase and hormonal communication systems
• Parts of the Nervous System

  • Central Nervous System (CNS)
  • Sensory Neurons
  • Motor Neurons
  • Effectors
• Central Nervous System (CNS)

  In vertebrates animals with backbones this consists of the brain and spinal cord only. In mammals, the CNS is connected to the body by sensory neurons and motor neurons
• Sensory Neurones


  The neurones that carry information as electrical impulses from the tors to the CNS
• Motor Neurons


  The neurons that can transfer electrical impulses from the CNS to effectors
• Effectors


  All your muscles and glands, which respond to nervous impulses
• Receptors and Effectors can form part of Complex Organs
• Receptors are the cells that detect stimul
• Effectors can form part of larger, complex organism
• Effectors respond in different ways to nervous impulses, wherean glands secrete hormon
• The Response


  The CNS a cursation.cone-it receives information from the receptors and then mone decides what to do about it). The response is carried out by effectors.
• Synapse


  • The connection between two neurones
  • The nerve signal is transferred by chemicals which diffuse (move) across the gap
  • These chemicals then set off a new electrical signal in the next neurone
• Reflexes


  • Rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain
  • They can reduce the chances of being injured
• Reflex Arc


  1. The neurones in reflex arcs go through the spinal cord or through an unconscious part of the brain

  2. When a stimulus (e.g. a painful bee sting) is detected by receptors, impulses are sent along a sensory neurone to the CNS

  3. When the impulses reach a synapse between the sensory neurone and a relay neurone, they trigger chemicals to be released

  4. These chemicals cause impulses to be sent along the relay neurone

  5. When the impulses reach a synapse between the relay neurone and a motor neurone, the same thing happens

  6. Chemicals are released and cause impulses to be sent along the motor neurone

  7. The impulses then travel along the motor neurone to the effector (in this example it's a musclel

  8. The muscle then contracts and moves your hand away from the bee
• Because you don't have to think about the response (which takes time) it's quicker than normal responses
• Reflexs trespass your conscious brain completely when a quick response is essential
• Reaction time


  • The time it takes to respond to a stimulus- it's often less than a second
  • It can be affected by factors such as age, gender or drugs
• Measuring Reaction Time


  1. The person being tested should sit with their arm resting on the edge of a uble (this should stop them moving their arm up or down during the test)

  2. Hold a nult vertically between their thumb and forefinger. Make sure that the zero end of the ruler is level with their thumb and finger. Then let go without giving any warning

  3. The person being tested should try to catch the ruler as quickly as they can-as soon as they see it fall

  4. Reaction time is measured by the number on the ruler where it's caught-the further down its caught lie. the higher the number), the slower their reaction time

  5. Rap the test several times then calculate the mean distance that the ruler fell

  6. The person being tested should then have a caffeinated drink eg 300 ml of colal. After ten minutes, repeat steps 1 to 5

  7. You need to control any variables to make sure that this is a fair test
• Too much caffeine can cause unpleasant side-effects, so the person being tested should wad dreking any completed
• Measuring Reaction Time Using a Computer

  1. Simple computer tests can also be used to sure action Sme

  2. Computers can give a more precise reaction time because they remove for example, the person being tested has to click the mouse (or press as soon as they see a stimulus on the screen, e.g. a box change colo

  3. As the computer can record reaction time in millisecond

  4. Using a computes can also remove the meas
• Hormones


  • Chemical messengers sent in the blood
  • They are carried in the blood to other parts of the body, but only affect particular cells in particular organs (called target organs)
  • They control things in organs and cells that need constant adjustment
  • They are produced in (and secreted by) various glands, called endocrine glands
  • They tend to have relatively long-lasting effects
• Endocrine Glands


  • Pituitary gland
  • Thyroid
  • Ovaries (females only)
  • Adrenal gland
  • Testes (males only)
  • Pancreas
• Pituitary gland


  • Produces many hormones that regulate body conditions
  • It is sometimes called the master gland because these hormones act on other glands, directing them to release hormones that bring about change
• Thyroid


  Produces hormones which are involved in regulating things like the rate of metabolism, heart rate and temperature
• Ovaries (females only)


  Produce oestrogen, which is involved in the menstrual cycle (see page 116)
• Adrenal gland


  Produces adrenaline, which is used to prepare the body for a fight or flight response (see page 12)
• Testes (males only)


  Produce testosterone, which controls puberty and sperm production in males (see page 115)
• Pancreas


  Produces insulin, which is used to regulate the blood glucose level (see page 112)
• If the Response is Really Quick, It's Probably Nervous
• If a Response Lasts For a Long Time, It's Probably Hormonal
• Insulin and Glucagon


  Hormones that control blood glucose level as part of homeostasis
• Insulin and Glucagon Control Blood Glucose Level

  1. Eating foods containing cadratedate puts glucose (a type of sugar) into the blood from the g

  2. The something moves much more glucose from the blood

  3. Glucose can be stored as glycogen in the liver and in the muscles

  4. The incase in the blood must be kept steady Changes are monitored and controlled the swing the hormones insulin and glucagon, in a negative feedback cycle